LASIK, or Laser-Assisted In Situ Keratomileusis, is widely known for correcting nearsightedness. The question of whether this technology can address farsightedness, also called hyperopia, often arises. Hyperopia is a refractive error where the eyeball is too short or the cornea is too flat, causing incoming light to focus behind the retina instead of directly on it, which typically makes near objects blurry. Fortunately, LASIK can correct hyperopia, though the underlying physics and surgical approach are fundamentally different from those used for nearsightedness.
The Mechanism of Hyperopia Correction
Correcting hyperopia with LASIK requires the excimer laser to perform the opposite adjustment needed for nearsightedness. For a farsighted eye, the cornea’s focusing power is insufficient, so the goal of the surgery is to increase that power. This increase is accomplished by steepening the central curvature of the cornea, which allows light rays to converge sooner and land precisely on the retina.
To achieve this steepening effect, the excimer laser removes corneal tissue in a unique ring-shaped pattern around the central area, known as peripheral ablation. By removing tissue from the outer portion of the treatment zone, the central cornea is effectively pulled tighter, increasing its curvature and refractive power. This differs from nearsightedness correction, which involves removing central tissue to flatten the cornea.
As is standard in LASIK, the surgeon first creates a thin, hinged flap on the cornea’s surface to access the underlying stroma. The excimer laser then applies the precise ablation pattern to the exposed tissue. Once reshaping is complete, the corneal flap is repositioned, where it adheres without stitches. The success of this mechanism depends on the laser’s ability to create a smooth, precisely curved central surface that correctly focuses the light.
The physics involved demand a highly sophisticated laser system because the optical zone for hyperopia correction is typically larger than for myopia. This larger treatment area ensures a smooth transition between the treated and untreated areas of the cornea. Without this careful blending, patients can experience visual disturbances, such as glare or halos, especially in low-light conditions.
Determining Suitability and Correction Limits
While LASIK can successfully correct hyperopia, the procedure has specific limitations that determine patient suitability. The range of farsightedness that can be effectively and stably corrected is narrower than the range for nearsightedness. Generally, LASIK is most effective for mild to moderate hyperopia, typically up to a maximum of about +4.00 diopters, though some advanced laser platforms may treat up to +6.00 diopters.
A necessary criterion for any LASIK procedure is a stable prescription, meaning the refractive error should not have changed by more than 0.5 diopters in the year leading up to the evaluation. Adequate corneal thickness is also required, as the laser ablation must be performed safely without compromising the cornea’s structural integrity. The patient’s natural corneal curvature must also be suitable for the necessary steepening.
A significant challenge associated with hyperopic LASIK, particularly for higher corrections, is the risk of regression. Regression is the gradual tendency for the eye to shift back toward its original hyperopic state over time, potentially requiring an enhancement procedure. This phenomenon is attributed to the eye’s natural healing response, specifically the remodeling of the corneal epithelium over the treated area.
This biological tendency means that long-term stability is a greater concern for hyperopic LASIK compared to myopic correction. Patients with higher prescriptions or specific anatomical features, such as thinner corneas, may be at an increased risk for this shift. Careful pre-operative screening is necessary to identify the best candidates and manage expectations regarding the long-term outcome.
Other Refractive Options for Farsightedness
When a patient’s hyperopia falls outside the safe or stable limits for LASIK, or if other eye health factors are present, alternative refractive procedures are available. These options correct the focusing error using different surgical approaches. One common alternative is Photorefractive Keratectomy, or PRK, which uses the same excimer laser technology as LASIK.
PRK involves reshaping the cornea directly on the surface after the outermost layer, the epithelium, is gently removed, rather than creating a flap. Because PRK does not require a flap, it is often recommended for patients with corneas too thin for LASIK. The recovery time is typically longer, as the epithelial layer must regenerate, but the final visual results are comparable to LASIK.
For older patients with higher degrees of farsightedness, Refractive Lens Exchange (RLE) is often a preferred solution. This procedure is identical to modern cataract surgery, involving the removal of the eye’s natural lens and replacing it with an artificial intraocular lens (IOL). RLE is especially advantageous for high hyperopia, often exceeding +4.00 diopters, as it provides a more permanent and stable correction that bypasses the limitations of corneal reshaping.
RLE also eliminates the possibility of future cataracts, which develop in the natural lens as a person ages. Modern IOLs can be selected to correct both distance vision and presbyopia, the age-related loss of near vision, making it a comprehensive choice for the aging farsighted eye. These alternatives ensure that a viable vision correction option exists for nearly every degree of hyperopia.